Device and method of handling power headroom report for multiple time intervals

ABSTRACT

A communication device for handling a power headroom report (PHR) for multiple transmission time intervals (TTIs) comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise determining a single PHR for a first TTI of at least one first serving cell according to at least one PH level of the at least one serving cell, wherein the communication device is configured with at least one second serving cell of at least one second TTI; and transmitting the PHR to a network via one of the at least one serving cell; wherein a length of the first TTI is different from each length of the at least one second TTI.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/660,962, filed on Jul. 27, 2017. The U.S. application Ser. No.15/660,962 claims the benefit of U.S. Provisional Application No.62/368,188 filed on Jul. 29, 2016, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a communication device and a methodused in a wireless communication system, and more particularly, to acommunication device and a method of handling a power headroom reportfor multiple time intervals in a wireless communication system.

2. Description of the Prior Art

A long-term evolution (LTE) system supporting the 3rd GenerationPartnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standardare developed by the 3GPP as a successor of the universal mobiletelecommunication system (UMTS) for further enhancing performance of theUMTS to satisfy increasing needs of users. The LTE system includes a newradio interface and a new radio network architecture that provides highdata rate, low latency, packet optimization, and improved systemcapacity and coverage. In the LTE system, a radio access network knownas an evolved universal terrestrial radio access network (E-UTRAN)includes at least one evolved Node-B (eNB) for communicating with atleast one user equipment (UE), and for communicating with a core networkincluding a mobility management entity (MME), a serving gateway, etc.,for Non-Access Stratum (NAS) control.

A LTE-advanced (LTE-A) system, as its name implies, is an evolution ofthe LTE system. The LTE-A system targets faster switching between powerstates, improves performance at the coverage edge of an eNB, increasespeak data rate and throughput, and includes advanced techniques, such ascarrier aggregation (CA), coordinated multipoint (CoMP)transmissions/reception, uplink (UL) multiple-input multiple-output(UL-MIMO), licensed-assisted access (LAA) (e.g., using LTE), etc. For aUE and an eNB to communicate with each other in the LTE-A system, the UEand the eNB must support standards developed for the LTE-A system, suchas the 3GPP Rel-1× standard or later versions.

A shortened transmission time interval (TTI) is proposed to improvedtransmission efficiency. However, the shortened TTI may coexist with alegacy TTI (i.e., normal TTI). That is, a UE may perform transmissionsvia both the shortened TTI and the legacy TTI. Transmission of a powerheadroom report in the art is developed only for the legacy TTI, andcannot be applied to TTIs with multiple types (e.g., lengths). Thus, howto handle the power headroom report for the TTIs is an important problemto be solved.

SUMMARY OF THE INVENTION

The present invention therefore provides a method and relatedcommunication device for handling a power headroom report for multipletime intervals to solve the abovementioned problem.

A communication device for handling a power headroom report (PHR) formultiple transmission time intervals (TTIs) comprises a storage devicefor storing instructions and a processing circuit coupled to the storagedevice. The processing circuit is configured to execute the instructionsstored in the storage device. The instructions comprise determining atleast one first PHR for a first TTI of at least one first serving cellaccording to at least one first PH level of the at least one firstserving cell, wherein the communication device is configured with atleast one second serving cell of at least one second TTI; andtransmitting the at least one first PHR to a network via one of the atleast one serving cell; wherein a length of the first TTI is differentfrom at least one length of the at least one second TTI.

A method for a communication device to handle a power headroom report(PHR) for multiple transmission time intervals (TTIs), comprisesdetermining at least one first PHR for a first TTI of at least one firstserving cell according to at least one first PH level of the at leastone first serving cell, wherein the communication device is configuredwith at least one second serving cell of at least one second TTI; andtransmitting the at least one first PHR to a network via one of the atleast one serving cell; wherein a length of the first TTI is differentfrom at least one length of the at least one second TTI.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communication systemaccording to an example of the present invention.

FIG. 2 is a schematic diagram of a communication device according to anexample of the present invention.

FIG. 3 is a flowchart of a process according to an example of thepresent invention.

FIG. 4 is a flowchart of a process according to an example of thepresent invention.

FIG. 5 is a flowchart of a process according to an example of thepresent invention.

FIG. 6 is a schematic diagram of determining a PHR for multiple timeintervals according to an example of the present invention.

FIG. 7 is a schematic diagram of determining a PHR for multiple timeintervals according to an example of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a wireless communication system 10according to an example of the present invention. The wirelesscommunication system 10 is briefly composed of a network and a pluralityof communication devices. The wireless communication system 10 maysupport a time-division duplexing (TDD) mode, a frequency-divisionduplexing (FDD) mode, a TDD-FDD joint operation mode or alicensed-assisted access (LAA) mode. That is, the network and acommunication device may communicate with each other via FDD carrier(s),TDD carrier(s), licensed carrier(s) (licensed serving cell(s)) and/orunlicensed carrier(s) (unlicensed serving cell(s)). In addition, thewireless communication system 10 may support a carrier aggregation (CA).That is, the network and a communication device may communicate witheach other via multiple serving cells (e.g., multiple serving carriers)including a primary cell (e.g., primary component carrier) and one ormore secondary cells (e.g., secondary component carriers).

In FIG. 1 , the network and the communication devices are simplyutilized for illustrating the structure of the wireless communicationsystem 10. Practically, the network may be a universal terrestrial radioaccess network (UTRAN) including at least one Node-B (NB) in a universalmobile telecommunications system (UMTS). In one example, the network maybe an evolved UTRAN (E-UTRAN) including at least one evolved NB (eNB)and/or at least one relay node in a long term evolution (LTE) system, aLTE-Advanced (LTE-A) system, an evolution of the LTE-A system, etc. Inone example, the network may be a next generation radio access network(NR-RAN) including at least one eNB and/or at least one next generationNB (gNB).

Furthermore, the network may also include at least one of theUTRAN/E-UTRAN/NG-RAN and a core network, wherein the core network mayinclude network entities such as Mobility Management Entity (MME),Serving Gateway (S-GW), Packet Data Network (PDN) Gateway (P-GW),Self-Organizing Networks (SON) server and/or Radio Network Controller(RNC), etc. In other words, after the network receives informationtransmitted by a communication device, the information may be processedonly by the UTRAN/E-UTRAN/NG-RAN and decisions corresponding to theinformation are made at the UTRAN/E-UTRAN/NG-RAN. Alternatively, theUTRAN/E-UTRAN/NG-RAN may forward the information to the core network,and the decisions corresponding to the information are made at the corenetwork after the core network processes the information. In addition,the information may be processed by both the UTRAN/E-UTRAN/NG-RAN andthe core network, and the decisions are made after coordination and/orcooperation are performed by the UTRAN/E-UTRAN/NG-RAN and the corenetwork.

A communication device may be a user equipment (UE), a low cost device(e.g., machine type communication (MTC) device), a device-to-device(D2D) communication device, a narrow-band internet of things (IoT)(NB-IoT), a mobile phone, a laptop, a tablet computer, an electronicbook, a portable computer system, or combination thereof. In addition,the network and the communication device can be seen as a transmitter ora receiver according to direction (i.e., transmission direction), e.g.,for an uplink (UL), the communication device is the transmitter and thenetwork is the receiver, and for a downlink (DL), the network is thetransmitter and the communication device is the receiver.

FIG. 2 is a schematic diagram of a communication device 20 according toan example of the present invention. The communication device 20 may bea communication device or the network shown in FIG. 1 , but is notlimited herein. The communication device 20 may include a processingcircuit 200 such as a microprocessor or Application Specific IntegratedCircuit (ASIC), a storage device 210 and a communication interfacingdevice 220. The storage device 210 may be any data storage device thatmay store a program code 214, accessed and executed by the processingcircuit 200. Examples of the storage device 210 include but are notlimited to a subscriber identity module (SIM), read-only memory (ROM),flash memory, random-access memory (RAM), Compact Disc Read-Only Memory(CD-ROM), digital versatile disc-ROM (DVD-ROM), Blu-ray Disc-ROM(BD-ROM), magnetic tape, hard disk, optical data storage device,non-volatile storage device, non-transitory computer-readable medium(e.g., tangible media), etc. The communication interfacing device 220 ispreferably a transceiver and is used to transmit and receive signals(e.g., data, messages and/or packets) according to processing results ofthe processing circuit 200.

FIG. 3 is a flowchart of a process 30 according to an example of thepresent invention. The process 30 may be utilized in a communicationdevice shown in FIG. 1 , to handle a power headroom report (PHR) formultiple time intervals. The process 30 may be compiled into the programcode 214 and includes the following steps:

Step 300: Start.

Step 302: Determine a PHR for a plurality of time intervals in a timeinterval according to a PH level of one of the plurality of timeintervals, wherein the plurality of time intervals comprises at leastone scheduled time interval.

Step 304: Transmit the PHR to a network.

Step 306: End.

According to the process 30, the communication device determines a PHRfor a plurality of time intervals (e.g., shortened time intervals) in atime interval (e.g., normal time interval) according to a PH level ofone of the plurality of time intervals. The plurality of time intervalsmay or may not comprise at least one scheduled time interval. Forexample, the PHR includes the PH level. That is, part or all of the timeintervals are scheduled for UL transmissions. Then, the communicationdevice transmits the PHR (e.g., including the PH level) to a network.That is, (e.g., only) one PH level is used for reporting the PHR to thenetwork to solve the problem in the art.

Realization of the process 30 is not limited to the above description.The following examples may be applied for realizing the process 30.

In one example, the one of the plurality of time intervals is a firstscheduled time interval of the at least one scheduled time interval.That is, the PHR is determined according to the PH level of the foremostscheduled time interval. In one example, the one of the plurality oftime intervals is a last scheduled time interval of the at least onescheduled time interval. That is, the PHR is determined according to thePH level of the tail scheduled time interval. In one example, the one ofthe plurality of time intervals is predetermined in the communicationdevice. That is, the PHR is determined according to the PH level of thepredetermined (e.g., preconfigured, configured) time interval. In oneexample, the one of the plurality of time intervals is a first timeinterval of the plurality of time intervals. In one example, the one ofthe plurality of time intervals is a last time interval of the pluralityof time intervals.

In one example, the PH level of the one of the plurality of timeintervals is lowest in at least one PH level of the at least onescheduled time interval. That is, the PHR is determined according to thelowest scheduled PH level. In one example, the PH level of the one ofthe plurality of time intervals is highest in at least one PH level ofthe at least one scheduled time interval. That is, the PHR is determinedaccording to the highest scheduled PH level. In one example, the PHlevel of the one of the plurality of time intervals is lowest in aplurality of PH levels of the plurality of time intervals. That is, thePHR is determined according to the lowest PH level. In one example, thePH level of the one of the plurality of time intervals is highest in theplurality of PH levels of the plurality of time intervals. That is, thePHR is determined according to the highest PH level. In one example, thePHR is determined according to an average of at least one PH level ofthe at least one scheduled time interval. That is, only scheduled timeintervals are included. In one example, the PHR is determined accordingto an average of a plurality of PH levels of the plurality of timeintervals. That is, all time intervals are included.

In one example, the communication device transmits the PHR and an indexof the one of the plurality of time intervals to the network. In oneexample, the communication device transmits the PHR in the time intervalto the network. In one example, the communication device transmits thePHR in one of the at least one scheduled time interval. Further, alength of the one of the at least one scheduled time interval is shorterthan at least one length of the rest of the at least one scheduled timeinterval.

In one example, the time interval is for performing at least one ULtransmission via a first cell, and the plurality of time intervals arefor performing a plurality of UL transmissions via at least one secondcell. Further, the at least one second cell belongs to at least one BSof the network. In one example, the time interval is for performing atleast one UL transmission via a first radio access technology (RAT), andthe plurality of time intervals are for performing a plurality of ULtransmissions via a second RAT. In one example, a plurality of lengthsof the plurality of time intervals are the same. In one example, each ofa plurality of lengths of the plurality of time intervals are notgreater than a half length of the time interval.

FIG. 4 is a flowchart of a process 40 according to an example of thepresent invention. The process 40 may be utilized in a communicationdevice shown in FIG. 1 , to handle a PHR for multiple time intervals.The process 40 may be compiled into the program code 214 and includesthe following steps:

Step 400: Start.

Step 402: Determine a first PHR for at least one first time interval ina time interval according to at least one first PH level of the at leastone first time interval, wherein the at least one first time intervalcomprises at least one first scheduled time interval.

Step 404: Determine a second PHR for at least one second time intervalin the time interval according to at least one second PH level of the atleast one second time interval, wherein the at least one second timeinterval comprises at least one second scheduled time interval.

Step 406: Transmit the first PHR and the second PHR to a network.

Step 408: End.

According to the process 40, the communication device determines a firstPHR for at least one first time interval in a time interval according toat least one first PH level of the at least one first time interval. Theat least one first time interval may or may not comprise at least onefirst scheduled time interval. The communication device determines asecond PHR for at least one second time interval in the time intervalaccording to at least one second PH level of the at least one secondtime interval. The at least one second time interval may or may notcomprise at least one second scheduled time interval. Then, thecommunication device transmits the first PHR (e.g., including the atleast one first PH level) and the second PHR (e.g., including the atleast one second PH level) to a network. For example, the first PHRincludes the at least one first PH level, and the second PHR includesthe at least one second PH level. That is, multiple PH levels are usedfor reporting the PHRs to the network to solve the problem in the art.

Realization of the process 40 is not limited to the above description.The following examples may be applied for realizing the process 40.

In one example, the communication device transmits the first PHR and thesecond PHR in one of the at least one first scheduled time interval tothe network. Further, a length of each of the at least one first timeinterval is shorter than a length of each of the at least one secondtime interval. That is, a shorter time interval is used for transmittingthe PHRs. In one example, the communication device transmits the firstPHR in one of the at least one first scheduled time interval to thenetwork, and transmits the second PHR in one of the at least one secondscheduled time interval to the network. That is, the PHRs aretransmitted in the respective time intervals.

In one example, the at least one first time interval and the at leastone second time interval are for performing a plurality of ULtransmissions via a cell. In one example, the at least one first timeinterval is for performing at least one first UL transmission via atleast one first cell, and the at least one second time interval is forperforming at least one second UL transmission via at least one secondcell. Further, the at least one first cell belongs to a first cell groupaccording to at least one length of the at least one first timeinterval, and the second cell belongs to a second cell group accordingto at least one length of the at least one second time interval. In oneexample, the at least one first cell and the at least one second cellbelong to a cell group according to a plurality of lengths of the atleast one first time interval and the at least one second time interval.In one example, the at least one first cell and the at least one secondcell belong to a BS of the network, or belong to different BSs of thenetwork. In one example, the at least one first time interval is forperforming at least one first UL transmission via a first RAT, and theat least one second time interval is for performing at least one secondUL transmission via a second RAT.

FIG. 5 is a flowchart of a process 50 according to an example of thepresent invention. The process 50 may be utilized in a communicationdevice shown in FIG. 1 , to handle a PHR for multiple time intervals.The process 50 may be compiled into the program code 214 and includesthe following steps:

Step 500: Start.

Step 502: Determine a PHR for a first time interval of at least onefirst serving cell according to at least one PH level of the at leastone serving cell, wherein the communication device is configured with atleast one second time interval of at least one second serving cell.

Step 504: Transmit the PHR to a network via one of the at least oneserving cell.

Step 506: End.

According to the process 50, the communication device determines a PHRfor a first time interval of at least one first serving cell accordingto at least one PH level of the at least one serving cell, wherein thecommunication device is configured with at least one second timeinterval of at least one second serving cell. Then, the communicationdevice transmits the PHR to a network via one of the at least oneserving cell. For example, the PHR includes the at least one PH level.That is, the PHR for the first time interval is transmitted, while atleast one PHR for the at least one second timer interval is notprocessed.

Realization of the process 50 is not limited to the above description.The following examples may be applied for realizing the process 50.

In one example, the communication device transmits the PHR to thenetwork via one of the at least one first serving cell. In one example,the communication device transmits the PHR and an index of the firsttime interval to the network. In one example, the first time interval isfor performing at least one first UL transmission via the at least oneserving cell, and the at least one second time interval are forperforming at least second UL transmission via the at least one secondserving cell. In one example, the first time interval is for performingat least one UL transmission via a first RAT, and the at least onesecond time interval is for performing at least second UL transmissionvia a second RAT. In one example, a length of the first time interval isdifferent from each length of the at least one second time interval.

The following examples may be applied for realizing the process 30, 40and/or 50.

It should be noted that lengths of the time intervals mentioned aboveare not limited. In one example, a length of the time interval is 0.5,1, 2, 3, 4 transmission time interval(s) (TTI(s)). A TTI may be 1 ms or2 ms, but is not limited herein. A PH level for a time interval (e.g.,shortened time interval) may be (e.g., a function of) a differencebetween a power level of the time interval and a power level limit of acell (e.g., serving cell) corresponding to the time interval. A timeinterval termed as a “scheduled” time interval means that a ULtransmission may be performed in the time interval or that the timeinterval is scheduled by the network to be performed in the timeinterval. In one example, the communication device transmits a PHRaccording to a reporting periodicity which is communicationdevice-specific, or according to a cell group of the PHR (e.g., timeinterval length group).

FIG. 6 is a schematic diagram of determining a PHR for multiple timeintervals according to an example of the present invention. Four ULtransmissions UT1-UT4 with power levels P1-P4 (e.g., scheduled powerlevels or calculated/determined power levels) are considered. Forexample, the UL transmission UT1 includes a physical UL shared channel(PUSCH), and the UL transmissions UT2-UT4 include PUSCH(s) and/orphysical UL control channel(s) (PUCCH(s)). The UL transmissions UT1-UT4are performed in time intervals T1-T4, respectively, wherein the timeintervals T2-T4 are shortened time intervals. The UL transmission UT1may be performed with a first serving cell, and the UL transmissionsUT2-UT4 may be performed with a second serving cell. In the presentinvention, power level limits PMAX1-PMAX2 are assumed for the timeintervals T1 and T2-T4, respectively. Accordingly, PH levels PV1-PV4 forthe time intervals T1-T4 can be determined, wherein PV1=PMAX1−P1,PV2=PMAX2−P2, PV3=PMAX2−P3 and PV4=PMAX2−P4 can be obtained. Therelation between the PH levels PV2-PV4 may be PV2>PV3>PV4.

In one example, the communication device determines a PHR according tothe PH level PV2 of the first time interval (e.g., the first scheduledtime interval). In one example, the communication device determines aPHR according to the PH level PV4 of the last time interval (e.g., thelast scheduled time interval). In one example, a predetermined timeinterval is the time interval T3, and the communication devicedetermines a PHR according to the PH level PV3. In one example, thecommunication device determines a PHR according to the lowest PH levelwhich is the PH level PV4. In one example, the communication devicedetermines a PHR according to the highest PH level which is the PH levelPV2.

In one example, the communication device determines a PHR according toan average of the PH levels PV2-PV4 which is (PV2+PV3+PV4)/3. In oneexample, only the time intervals T2 and T4 are scheduled for thecommunication device, while the time interval T3 is not (i.e., P3=0).The communication device may determine a PHR according to an average ofthe PH levels PV2 and PV4 which is (PV2+PV4)/3. That is, only thescheduled time intervals are considered. Alternatively, thecommunication device may still determine a PHR according to an averageof the PH levels PV2-PV4 which is (PV2+PV3+PV4)/3. That is, the timeinterval T3 which is not scheduled is still considered.

FIG. 7 is a schematic diagram of determining a PHR for multiple timeintervals according to an example of the present invention. Four ULtransmissions UT1-UT4 with power levels P1-P4 (e.g., scheduled powerlevels or calculated/determined power levels) are considered. Forexample, each of the UL transmissions UT1-UT4 includes a PUSCH or aPUCCH. The UL transmissions UT1-UT4 are performed in time intervalsT1-T4, respectively, wherein the time intervals T3-T4 are shortened timeintervals. The UL transmissions UT1-UT4 may be performed with a firstserving cell, a second serving cell, a third serving cell and a fourthserving cell, respectively. In the present invention, power level limitsPMAX1-P MAX 4 are assumed for the time intervals T1-T4, respectively.Accordingly, PH levels PV1-PV4 for the time intervals T1-T4 can bedetermined, wherein PV1=PMAX1−P1, PV2=PMAX2−P2, PV3=PMAX2−P3 andPV4=PMAX2−P4 can be obtained.

In one example, the PHR for the serving cells determined according thePH levels PV1-PV4 may be transmitted in a shorter time interval. Forexample, the PHR for all the serving cells may be transmitted via thetime interval T3 or T4. In another example, the PHR may be transmittedaccording to cell groups determined according to lengths of the timeintervals T1-T4. For example, the PHR for the first serving cell and thesecond serving cell may be transmitted in the time interval T1 (e.g., tothe first serving cell) or the time interval T2 (e.g., to the firstserving cell), because the lengths of the time intervals T1 and T2 arethe same. In addition, the PHR for the third serving cell and the fourthserving cell may be transmitted in the time interval T3 (e.g., to thethird serving cell) or the time interval T4 (e.g., to the fourth servingcell), because the lengths of the time intervals T3 and T4 are the same.

It should be noted that when the PHR is transmitted in a correspondingtime interval (e.g., corresponding cell group), part of the PHR may bedropped. For example, part of the PHR for the first serving cell and thesecond serving cell (which is related to the PH levels PV1 and PV2) istransmitted, while part of the PHR for the third serving cell and thefourth serving cell (which is related to the PH levels PV3 and PV4) isdropped. That is, the PHR for the shortened time intervals are nottransmitted.

In the above examples, a power level may mean transmission power orpower related to a communication operation. A scheduled power level fora UL transmission may be any power level obtained prior the execution ofthe processes 30 and 40, For example, the scheduled power level may be apower level scheduled (e.g., indicated) by the network, may be a powerlevel predetermined in (e.g., calculated by) the communication device,and is not limited herein. “PH level” may be termed as “PH”.

Those skilled in the art should readily make combinations, modificationsand/or alterations on the abovementioned description and examples. Theabovementioned description, steps and/or processes including suggestedsteps can be realized by means that could be hardware, software,firmware (known as a combination of a hardware device and computerinstructions and data that reside as read-only software on the hardwaredevice), an electronic system, or combination thereof. An example of themeans may be the communication device 20.

Examples of the hardware may include analog circuit(s), digitalcircuit(s) and/or mixed circuit(s). For example, the hardware mayinclude ASIC(s), field programmable gate array(s) (FPGA(s)),programmable logic device(s), coupled hardware components or combinationthereof. In another example, the hardware may include general-purposeprocessor(s), microprocessor(s), controller(s), digital signalprocessor(s) (DSP(s)) or combination thereof.

Examples of the software may include set(s) of codes, set(s) ofinstructions and/or set(s) of functions retained (e.g., stored) in astorage unit, e.g., a computer-readable medium. The computer-readablemedium may include SIM, ROM, flash memory, RAM, CD-ROM/DVD-ROM/BD-ROM,magnetic tape, hard disk, optical data storage device, non-volatilestorage unit, or combination thereof. The computer-readable medium(e.g., storage unit) may be coupled to at least one processor internally(e.g., integrated) or externally (e.g., separated). The at least oneprocessor which may include one or more modules may (e.g., be configuredto) execute the software in the computer-readable medium. The set(s) ofcodes, the set(s) of instructions and/or the set(s) of functions maycause the at least one processor, the module(s), the hardware and/or theelectronic system to perform the related steps.

Examples of the electronic system may include a system on chip (SoC),system in package (SiP), a computer on module (CoM), a computer programproduct, an apparatus, a mobile phone, a laptop, a tablet computer, anelectronic book or a portable computer system, and the communicationdevice 20.

To sum up, the present invention provides a device and method forhandling a PHR for multiple time intervals. Thus, a communication devicecan transmit the PHR to a network. As a result, the network can schedulethe communication device properly according to the PHR.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A communication device for handling a powerheadroom report (PHR) for multiple transmission time intervals (TTIs),comprising: a storage device, for storing instructions of: determining afirst PHR for a first TTI of a first serving cell according to a firstPH level of the first serving cell, wherein the communication device isconfigured with a second serving cell of a second TTI and a thirdserving cell of a plurality of third TTIs in the second TTI; determininga second PHR for the second TTI of the second serving cell according toa second PH level of the second serving cell; determining a third PHRfor a plurality of third TTIs of the third serving cell in the secondTTI according to a third PH level of one of the plurality of third TTIs;and transmitting the first PHR, the second PHR and the third PHR to anetwork via one of the first serving cell, the second serving cell andthe third serving cell; wherein at least one first serving cell is forperforming at least one first UL transmission via a first radio accesstechnology (RAT), and the second serving cell and the third serving cellare for performing at least one second UL transmission via a second RAT;wherein each length of the plurality of third TTIs is not greater than ahalf length of the second TTI; and a processing circuit, coupled to thestorage device, configured to execute the instructions stored in thestorage device.
 2. The communication device of claim 1, wherein thefirst TTI is for performing the at least one first UL transmission viathe first RAT, and the at least one second TTI is for performing the atleast second UL transmission via the second RAT.
 3. The communicationdevice of claim 1, wherein each of at least one length of the at leastone second TTI is not greater than a half length of the first TTI. 4.The communication device of claim 1, wherein a length of the first TTIis different from at least one length of the at least one second TTI. 5.The communication device of claim 1, wherein the one of the plurality ofthird TTIs is predetermined in the communication device.
 6. Thecommunication device of claim 1, wherein the plurality of third TTIsoccur in the second TTI.
 7. The communication device of claim 1, whereinthe first TTI is for performing the at least one first UL transmissionvia the first serving cell, and the second TTI and the one of theplurality of third TTI are for performing the at least second ULtransmission via the second serving cell and the third serving cell. 8.A method for a communication device to handle a power headroom report(PHR) for multiple transmission time intervals (TTIs), comprising:determining a first PHR for a first TTI of a first serving cellaccording to a first PH level of the first serving cell, wherein thecommunication device is configured with a second serving cell of asecond TTI and a third serving cell of a plurality of third TTIs in thesecond TTI; determining a second PHR for the second TTI of the secondserving cell according to a second PH level of the second serving cell;determining a third PHR for a plurality of third TTIs of the thirdserving cell in the second TTI according to a third PH level of one ofthe plurality of third TTIs; and transmitting the first PHR, the secondPHR and the third PHR to a network via one of the first serving cell,the second serving cell and the third serving cell; wherein at least onefirst serving cell is for performing at least one first UL transmissionvia a first radio access technology (RAT), and the second serving celland the third serving cell are for performing at least one second ULtransmission via a second RAT; wherein each length of the plurality ofthird TTIs is not greater than a half length of the second TTI.
 9. Themethod of claim 8, wherein the first TTI is for performing the at leastone first UL transmission via the first RAT, and the at least one secondTTI is for performing the at least second UL transmission via the secondRAT.
 10. The method of claim 8, wherein each of at least one length ofthe at least one second TTI is not greater than a half length of thefirst TTI.
 11. The method of claim 8, wherein a length of the first TTIis different from at least one length of the at least one second TTI.12. The method of claim 8, wherein the one of the plurality of thirdTTIs is predetermined in the communication device.
 13. The method ofclaim 8, wherein the plurality of third TTIs occur in the second TTI.14. The method of claim 8, wherein the first TTI is for performing theat least one first UL transmission via the first serving cell, and thesecond TTI and the one of the plurality of third TTI are for performingthe at least second UL transmission via the second serving cell and thethird serving cell.